The shaping of gemstones is akin to the shaping of optical lenses and is the work of the lapidarist who employes methods of grinding, sanding and polishing. More particularly, the shaping of a cabochon is akin to the shaping of an anastigmatic lens, a lens having an ovoid surface. Accordingly, the prior art practice of grinding such lenses, for example corrective lenses for eye glasses, has evolved from a rather simple arrangement of longitudinally offset axes to the present day refinement involving laterally offset axes and a complex of machinery for simultaneously generating ground surfaces about two right angularly related axes adjustably offset with respect to each other. The ovoid surface of such a lens is not so pronounced as that of a cabochon, however the principles of grinding are the same. And, though attempts have been made to mechanize the grinding of cabochons, they have been wanting in many respects because with simplification the desirable wide ranges of adjustment have been lost or sacrificed. Therefore it is a general object of this invention to provide a simple and yet practical cabochon generating device which has a wide range of selective adjustment. That is, a large number of different curvature relationships are generated thereby.
In the past, cabbing has involved the manipulation of a dop-stick to which the rough gemstone is dopped or attached, the configuration of the cabochon being entirely dependent upon the expertise of the artisan. Consequently, such cabochons vary widely in shape and are most often imperfect to some extent, in that they are seldom a true spheroid or ovoid. That is, inspection will show that a hand fashioned cabochon is asymmetrical to some extent and exhibits irregularities. Therefore, it is an object of this invention to provide a device for ensuring symmetry in a cabochon and to virtually eliminate surface irregularities.
A cabochon or "cab" is a flattened gemstone usually of oval form and having at least one convex side. Optimum convex curvature is uniformly developed about two right angularly related axes, presenting a symmetrical ovoid surface. Heretofore, ovoid lens surfaces have been generated by machines comprised of infinitely adjustable levers pivotally carrying the workpiece to be cut about two offset axes, the offset being infinitely adjustable as well. Such machines are complex in order to discriminately arrive at precise optical values. Applicant has observed that the principle of offset right angularly related axes about which levers of different radii control the surface contours of lens grinding is applicable to the generation of cabochons having the same geometric form, a convex spheroid or ovoid surface. Accordingly, it is an object of this invention to provide a simplified machine device having a positive rule of action replacing the manipulation of a dop-stick by an artisan, and to produce symmetrical cabochons without irregularities.
The truncation of the ovoid surface determines the plan form of the cabochon, and therefore it is desirable that the ovoid surface be true, otherwise the said plan form will not be a true circle or oval form. In other words, odd egg shapes and pear shapes are to be avoided. However, the ovoid proportions can vary widely with respect to the curvatures about the major and minor axes thereof, and accordingly it is an object of this invention to provide a wide range of pre-determined incremental relationships between the major and minor axis curvatures. With the present invention, both the major and minor curvatures and the offset relationship of the two axes are incrementally adjustable, and with the embodiment shown seventeen distinctly different cabs are produced as hereinafter shown and described.
The classic cabochon is of oval plan form configuration, however they are also formed as rounds, squares, polygons and random shapes. In all cases however a perfect convex surface is highly desirable, without undercuts and/or irregularities. Therefore, it is the convex surface with which this invention is concerned, and in practice several basic spherical surfaces are generated, as well as a number of ovoid surfaces. Therefore, there are instances where the two axes of generation intersect right angularly, and there are also instances where they are offset so as to generate the major and minor axes of the cabochon surface. It is the placement of axes with which this invention is particularly concerned, seventeen distinct cabochon configurations being generated with five incrementally spaced pivot openings in the dop-head arm and four incrementally spaced pivot openings on the pivot hub which advanceably offers the workpiece forwardly into cutting engagement with an abrasive wheel. Selective adjustment of the dop-head arm simultaneously determines the radii from said two axes of rotation. Basically, there is an advanceably movable vertical axis about which the major axis of the cabochon is generated, and there is an incrementally adjustable horizontal axis about which the minor axis of the cabochon is generated.
The art of shaping a cab involves "dopping" the rough stone onto the head end of a stick, and in the present machine to an arm. Such a stick is manipulated and fashioned in different manners to suit the artisan while the present arm is a permanent part of the machine. Further, the artisan working with the classic dop-stick and with the instant machine device can advantageously progress from the use of the dop-stick to said machine device. Furthermore, the artisan most often works upon a large number of art pieces or projects, so that interchangeability is highly desirable. Therefore, it is an object of this invention to provide replaceable dop-heads keyed to the dop-head arm of the present machine for exact positioning thereon, said dop-heads being replaceable at the active end of both a dop-stick and said dop-head arm of the machine. In practice, the replaceable dop-heads are fashioned to the standarized oval configuration plan forms of the cabs to be shaped, in two basic sizes.
The machine device of the present invention is primarily useful in the production of conventional cabochons wherein the major radius of curvature extends across the major axis of the oval form, and wherein the minor radius extends across the minor axis. Accordingly, the minor axis pivot is offset forwardly from the major axis pivot while the minor axis of the cab form parallels the major axis pivot, and the major axis of the cab form parallels the minor axis pivot. However, it is an object of this invention to create an inovation wherein the above described convention is reversed, so that the larger curvature extends transversely and the shorter curvature extends longitudinally of the cab oval. Accordingly, the pivot of this machine device is reversible so that the major axis pivot is offset rearwardly from the minor axis pivot while the major and minor axes of the cab form remain in the same rotative position keyed by the aforementioned cab head to the dop-head arm.